Actuatable structures, including miniature actuatable structures, are generally known in the art. In typical implementations, in the case of miniature structures, the structures are electrostatically actuated. According to one conventional configuration, an actuatable structure includes a stationary electrode and a movable member suspended at a distance from the stationary electrode. In some instances the movable member acts as a second electrode. Applying a drive voltage across the movable and stationary electrodes generates an electrical field between them. Electrostatic forces created by the field cause the movable member to deflect toward the stationary electrode. Varying the drive voltage varies the magnitude of the deflection.
One drawback of actuatable structures of this type is that they can suffer from a lack of linearity between the drive voltage and the resulting displacement of the movable member. This makes it difficult to control displacement. Another drawback is that they typically have characteristic instabilities. These instabilities can cause the movable member to be suddenly pulled into contact with the stationary electrode when the drive voltage exceeds a particular limit. Both the nonlinearities and instabilities tend to reduce the range of controllable, and thus usable, displacement of the movable member.
In another conventional approach, a first electrical conductor is formed on a carrier. A second electrical conductor having an electrically insulating lining is also formed on the carrier as a diaphragm over the first electrical conductor. A hollow space is created between the insulating lining and the first electrical conductor. The drive voltage is applied between the first and second electrical conductors to electrostatically deflect the diaphragm, and thus the insulating lining, toward the second electrical conductor. In the event that the first electrical conductor is deflected sufficiently to eliminate the hollow space, a gas is fed into the structure to deflect the first electrical conductor and insulating layer back to its original position. In other examples, gas is fed into the hollow space to prevent the hollow space from being eliminated.
A significant drawback of this approach is that the use of an injected gas complicates the design and makes it considerably more expensive. Another drawback is the insulator located on the inside of the diaphragm. Repeated movement of the diaphragm can cause the insulating material to crack and/or separate from the first electrical conductor. Differences between thermal coefficients of the insulating material and the first conductor may also cause the insulator to crack and/or separate from the first conductor. Any failure of the insulating layer can lead to a short between first and second conductors, and thus device.
A disadvantage of both prior art approaches discussed above is that they are formed by conventional techniques, such as masking, photolithography, chemical etching and/or reactive ion etching. All of these processes limit the types of materials that may be used, the types of mechanical structures that may be formed, and also the size of the mechanical structures that may be formed.
Accordingly, there is a need for both improved actuatable structures and methodologies for making them.